Photon diffusion in microscale solids.

Area of Science:

• Materials Science
• Thermal Physics
• Laser-Material Interactions

Background:

• Microscale materials exhibit unique thermal properties.
• Accurate heat transfer modeling is crucial for predicting material behavior under extreme conditions.
• Previous models often overlooked photon diffusion in highly absorbing materials.

Purpose of the Study:

• To investigate photon diffusion in microscale graphite under laser heating.
• To develop and validate a theoretical model incorporating photon diffusion.
• To explain discrepancies in previous thermal conductivity measurements.

Main Methods:

• Experimental heating of graphite samples (40 μm, 100 μm) using a Nd:YAG laser.
• High-speed pyrometry to record temperatures reaching thousands of kelvins.
• Solving the heat conduction equation with incorporated photon diffusion and lattice vibrations.

Main Results:

• Numerical simulations closely matched experimental data when photon diffusion was included.
• No fitting constants were required, validating the model with existing material properties.
• Photon diffusion was identified as the dominant heat transfer mechanism near evaporation temperatures.

Conclusions:

• Photon diffusion is a critical, often overlooked, heat transfer mechanism in microscale structures.
• This model resolves discrepancies between theoretical predictions and experimental thermal conductivity measurements.
• Understanding photon diffusion is essential for accurate thermal management of microscale materials.